Filtering face-piece respirators are distinguishable from other respiratory masks in that the mask body itself functions as the filtering mechanism. Unlike respirators that use rubber or elastomeric mask bodies in conjunction with attachable filter cartridges (see, e.g., U.S. Pat. No. RE39,493 to Yuschak et al.) or insert-molded filter elements (see, e.g., U.S. Pat. No. 4,790,306 to Braun), filtering face-piece respirators are fashioned to have the filter media comprise much of the whole mask body surface so that there is no need for installing or replacing a filter cartridge. As such, filtering face-piece respirators are relatively light in weight, easy to use, and are disposable. Examples of filtering face-piece respirators are shown in the following U.S. Pat. No. 7,131,442 to Kronzer et al, U.S. Pat. Nos. 6,923,182 and 6,041,782 to Angadjivand et al., U.S. Pat. Nos. 6,568,392 and 6,484,722 to Bostock et al., U.S. Pat. No. 6,394,090 to Chen, U.S. Pat. No. 4,807,619 to Dyrud et al., U.S. Pat. No. 4,536,440 to Berg, and in U.S. Patent Application Publication 2009/0078265A1 to Martin et al.
Workers regularly wear filtering face-piece respirators to protect themselves from inhaling airborne contaminants or to protect other persons or things from being exposed to pathogens and other contaminants exhaled by the wearer. Doctors, for example, commonly wear a respirator in an operating room to protect the patient from infection. In addition to removing airborne contaminants from inhale and exhale airstreams, filtering face-piece respirators also are worn to protect the wearer from splash fluids. An emergency room worker, for instance, can be exposed to blood ejected from a severed artery. Thus, some filtering face-piece respirators must properly satisfy the dual function of filtering air and stopping splash fluids. These dual functions, however, can be at odds with each other. Stopping fast moving liquid streams generally requires a fluid impermeable surface, whereas, air filtration demands fluid permeability at a low pressure drop.
“Pressure drop” is a term that refers to a difference in air pressure on both sides of the filter media or mask body. Lower pressure drops are desired in filtering face piece respirators so that the wearer need not work as hard to bring air or oxygen into their system. Since it is the wearer's lungs that pull the ambient air through the filtering face-piece, when there is less pressure drop, the wearer does not need to work as hard to breathe clean air. Low pressure drops are particularly desired by workers who wear filtering face piece respirators over extended time periods.
Because the dual function of stopping splash fluids and removing contaminants from ambient air are generally at odds with each other, investigators are presented with dilemma in fashioning a product that can deliver both splash fluid protection and air filtration without sacrificing pressure drop.